Study on shear characteristics and microscopic mechanism of rock joint reinforced by MICP

The microbial induced calcium carbonate precipitation (MICP) technology addresses the shortcomings of traditional reinforcement methods, such as poor fluidity, high energy consumption, and environmental pollution, and is gradually being applied to reinforce rock joint. The rock joint was grouted using a self-designed infusion device to obtain the shear mechanical and failure characteristics under different reinforcement cycles, cementation solution concentrations and normal stresses. The microscopic mechanisms were comprehensively analyzed using ultrasonic testing, scanning electron microscopy (SEM), X-ray diffractometer (XRD) and high-resolution transmission electron microscopy (HRTEM) technologies. The results show that the shear strength of the specimens gradually increased with the increase in reinforcement cycles and normal stress, while the shear strength initially increased and then decreased with the increase in cementation solution concentration. The shear failure of the rock joints mainly included failure between calcium carbonate, between calcium carbonate and rock particles, and between rock particles. Under the conditions of 20 reinforcement cycles, 1 mol/L cementation solution concentration, and 1 MPa normal stress, the failure area of the specimens was relatively small. The variation range of the sonic time values of the specimens was 34 to 50 μs, and the statistical patterns under different factors were consistent with the shear test results. The microscopic analysis explained that the improvement in shear strength was due to the well-developed calcite crystal form and its high proportion. By combining the MICP reinforcement process and the shear failure process, the influence mechanism of the evolution behavior of local rupture of microscopic crystals on the macroscopic shear failure process of the rock joint was revealed. This study can provide a reference basis for the formulation and optimization of rock mass reinforcement engineering schemes.